The present invention relates generally to security or locking devices for wheeled vehicles, and is particularly concerned with a locking device for a shopping cart.
Wheeled shopping carts are conventionally provided by supermarkets and other large stores for the convenience of shoppers, so that relatively large loads of goods can be collected, paid for, and then wheeled out to the shopper's vehicle for unloading. The empty cart is then collected by store personnel and returned to the store for subsequent use. The problem with this system is that carts are often removed from the store parking lot, for various reasons. One reason for such removal is that a shopper with no vehicle will use the cart to transport goods back to their home, and then often does not return the cart. This can result in permanent loss or theft of the cart. Loss of shopping carts adds significantly to the cost of operating stores or markets, since each cart is a relatively expensive item.
Numerous proposals have been made in the past for devices to deter shoppers or others from removing carts from the immediate vicinity or parking lot of a store. Such devices typically include some type of wheel locking mechanism which is activated when the cart crosses a boundary of some type around the perimeter of the parking lot. Up to now, these devices have had significant disadvantages and have not been adopted to any great extent due to the disadvantages or problems in implementing them. For example, some mechanisms are highly complex and liable to failure or improper operations. Other such mechanisms are too easy to circumvent to be effective. Some locking mechanisms are too difficult to deactivate when the cart is removed to the proper area. Others are liable to cause damage to the cart wheels or the ground surface when deployed. In other cases, the locking devices are so expensive that they add considerable cost to the carts. Another problem with such devices is that store personnel retrieving carts and nesting them together will have no way of knowing which carts have locked wheels. When the resultant "snake" of carts is pushed back to the store, locked wheels slide on the ground and are liable to be damaged.
One prior art locking device is described in U.S. Pat. No. 4,609,075 of Snedeker. This device comprises a ground contacting probe which is deployed by a magnetic triggering assembly when the cart is rolled over a magnetic strip at an outer perimeter of the parking area. The probe contacts the ground and lifts an adjacent cart wheel off the ground, disabling the cart. However, if a person attempts to push the cart at this point, dragging the probe along the ground, damage to the ground surface and probe may occur.
In U.S. Pat. No. 5,394,962 of Gray, a braking device for a wheeled vehicle includes a braking member which contacts the ground and lifts the vehicle to impede further movement. Again, the device is triggered by a magnet to release a blocking member, allowing the braking member to move into an activated position. Other shopping cart braking devices include stops which extend into openings in one or more wheels, preventing rotation of the wheel. Again, the locked wheel may then be dragged along the ground if a person still attempts to push the cart, damaging the tire.